A ladder type filter with resonators arranged in the form of a ladder is used in radio communications such as cellular phone communications. The ladder type filter realizes a bandpass filter that passes signals having desired frequencies. The bandpass filter is required to suppress signals having frequencies away from the pass band such as harmonic components that are the second harmonics of the pass band (that is, the desired frequencies), the third harmonics and so on.
As a method for suppressing the harmonic components of the pass band, there is known a method using a lumped constant LC resonance circuit or a distributed constant transmission line (Patent Document 1).
Patent Document 1 Japanese Patent Application Publication No. 2003-198325